Frescobaldi does not work

Version 3.1.3 of Frescobaldi just does not work; it throws lots of type errors. What you have to do is:

1. sudo apt purge frescobaldi
2. sudo apt install python3-ly python3-sip
3. sudo apt-mark auto python3-ly python3-sip
4. Download version 3.0.0 from https://ubuntu.pkgs.org/20.04/ubuntu-universe-amd64/frescobaldi_3.0.0+ds1-2_all.deb.html
   You have to scroll a long way down the page to find the actual .deb file.
5. cd $download_dir; sudo dpkg -i frescobaldi_3.0.0+ds1-2_all.deb
6. Under your own user ID rm -rf ~/.config/frescobaldi
   This will remove some settings that have been stored as floats instead of as integers; the new Frescobaldi will choke on them.
7. Posssibly apt install --fix-broken, depending on whether you see errors on first running frescobaldi.
8. Check that lilypond is installed, if not sudo apt install lilypond